A Solar Flares and CMEs as Drivers of Cosmic Ray Intensity Variations : A Comparative Analysis Across Solar Cycles 23-25

Abstract

Cosmic ray intensity variations near Earth are influenced by long-term solar cycle modulation and short-term transient disturbances originating from solar activity. Among the most significant drivers are solar flares and coronal mass ejections (CMEs), which alter the heliospheric magnetic field and solar wind conditions, thereby affecting the transport of galactic cosmic rays (GCRs). In this study, we present a comparative investigation of the impact of solar flares and CMEs on cosmic ray intensity variations during Solar Cycles 23-25. Neutron monitor observations from the Oulu station are employed as a proxy for GCR intensity, while solar flare and CME event catalogues are used to identify associated transient decreases such as Forbush decreases (FDs). A physically motivated association criterion based on interplanetary propagation delay is applied to connect solar events with cosmic ray responses. The results demonstrate that CME-associated events produce stronger and more sustained cosmic ray suppressions than flare-only events, indicating the dominant role of CME-driven shocks and magnetic clouds in generating Forbush decreases. Cycle-wise comparison shows clear differences: Solar Cycle 23 exhibits higher frequency and larger magnitude decreases, Solar Cycle 24 shows comparatively weaker modulation signatures, and Solar Cycle 25 reveals gradually increasing effects during its rising phase. The findings improve the understanding of cosmic ray modulation mechanisms and contribute to space weather research by clarifying the relative roles of flares and CMEs over multiple solar cycles.